The present invention relates generally to an ink cartridge and more particularly to an ink cartridge which is suitable for being mounted on a carriage for carrying an ink jet type recording head.
An ink jet recording apparatus such as an ink jet printer comprises an ink jet type recording head carried on a carriage in which pressure is applied to a pressure generating chamber. This chamber is maintained in fluid communication with a common ink tank on one side of the chamber and a nozzle opening on an other. Ink droplets are discharged from the nozzle opening upon the generation of pressure in the chamber. An ink cartridge comprising either the common ink tank or the common ink tank and a plurality of chambers and nozzle openings may be carried on the carriage for supplying the recording head with ink. This ink cartridge is constructed so that ink droplets are discharged onto a recording medium in response to printing data as the carriage is reciprocally moved.
Since the nozzle opening of the recording head is located at a position lower than the ink level in the ink cartridge, fluid pressure of the ink acts on the nozzle opening. A porous material is generally contained in the ink cartridge so that surface tension caused by the porous material allows the pressure inside the ink cartridge to be slightly lower than that at the nozzle opening in order to prevent ink from oozing out from the nozzle opening.
However, as ink is gradually consumed during printing operations and a smaller amount of ink remains absorbed in the porous material, the surface tension caused by the porous material becomes larger and makes it difficult to supply ink to the recording head. Thus, all ink contained in the cartridge will not be completely consumed.
Also, because of the porous material contained in the ink cartridge, the amount of ink stored in the ink cartridge is less than the volume of the ink cartridge by the actual total volume of the porous material. To compensate for the decreased amount of ink in a cartridge employing porous material, a larger ink cartridge is required than would be if the porous material were not employed in order to hold the same amount of ink.
To solve the problem mentioned above, an ink cartridge for an ink jet cording head, for example, as shown in U.S. Pat. No. 4,677,447 (based upon JP-A-62-231759), has been proposed. This patent shows an ink tank that is separated into two chambers by a wall formed with a through hole in a lower portion thereof. Ink is provided to the recording head from the first chamber. An umbrella check valve is movably arranged in the through hole. When the ink pressure on the ink head is decreased by expulsion of ink from the chamber, the umbrella check valve is opened to discharge the ink from the into to the cavity, and it is then supplied to the recording head from the first chamber into the second chamber, and it is then supplied to the recording head from the second chamber cavity.
According to the above-mentioned ink cartridge, aporous material need not be contained in the cartridge, so that a larger amount of ink can be substantially stored in the ink cartridge. However, use of the umbrella check valve raises another problem, since its offset amount is too large to finely adjust the amount of ink to be supplied to the recording head. Thus, fluctuations in the amount of ink supplied are caused and the printing quality is degraded.
In addition, since the ink in the first chamber is completely blocked from the recording head when the umbrella check valve is closed, if some change in environmental factors or temperature causes the volume of ink in the second chamber to increase as little as two to five percent, the pressure in the first chamber could increase and break the seal on a connection port which couples the ink cartridge to the recording head. The ink could then leak from the broken seal. Further, when the cartridge is mounted on the recording head, this increased pressure acts on the recording head whereby negative pressure cannot be maintained between the recording head and the ink tank, and thus ink could leak from the recording head.
Furthermore, the umbrella check valve is maintained in a closed state with a pressure difference of approximately 50 mmAq in order to ensure a stable supply of ink to the recording head. However, since this valve closing force is small, the umbrella check valve may open in response to a swinging motion of ink in the ink tank due to the movement of the carriage resulting in temporary pressure differences against the valve from the movement. Thus, stable printing may not be provided.
Additionally, if air enters a recording head while ink is being supplied thereto, the pressure for discharging ink droplets may be absorbed by the air bubble occurring within an ink passage of the recording head. Thus, defective printing may arise when the ink cartridge is exhausted. This problem may also arise if an ink cartridge is removed from a recording head if the ink is not depleted.
Accordingly, it is desirable to provide an ink cartridge which is capable of reliably supplying a recording head with ink in response to a minute pressure difference between the recording head and the ink cartridge, while maintaining negative pressure suitable for printing between the recording head and the ink cartridge, without being influenced by any swinging motion of ink contained therein due to the movement of a carriage upon which the recording head is mounted, and is also capable of preventing ink from leaking from an ink supply port of the cartridge leading to the recording head, or leaking from the recording head, due to temperature or other atmospheric changes.
Additionally, it is desirable to provide an ink cartridge which can prevent air from being drawn into the recording head at the time ink in the ink cartridge is exhausted, or if the ink cartridge is removed before all of the ink is depleted.